Catalytic treatment of industrial gases



April 1, 1952 F. w. HAYWOOD ETAL 2,591,543

CATALYTIC TREATMENT OF INDUSTRIAL GASES Original Filed Aug 30, 1945 72 8((91 '26 404,0 Jazalas 6.

Alto/m e g Patented Apr. 1, 1952 s-rA -ras PATENT CATALYTICmniTMEm'or'musmiin GASES February 28, 1945 This invention is forimprovements in or relating'to the removal of carbon dioxide fromindustrial carbonaceous gases utilising a catalyst s ;s ai.m .d..in 0.1m n ins app ica n. seri No. 613,572, filed August 30 l9 i5, lSSllQdJLIIY B, 1.94 8; asfPat'ent. No. 2,444,930, of which this is 6 Claims.

a division andhas for an object to provide a pro'eess'for the removal ofcarbon dioxide, oxy- (c1. tea -'2 i gen and sulphur-containing gasesfromindustrial gases such as towns 'gas and other carbonaceous gasesfused in industry for the formation for example offcarb'urisingatmospheres for the treatment'of ferrous alloys. i V

The constituents in such industrial gases which are the most valuablefor effecting carburising are ca'rbon' monoxide and methane and theremo'v'srof carbon dioxide and oxygen from gases contaihingalsocarbonmonoxide and methane has presented a problem of some diff cultysince the destruction of carbon monoxide and methane is whollyundesirable;

awarding to' our co-pending application Serial No. 613,572 there isprovided a catalyst consistmg, essentially of'barium carbonate extendedwith" 'fibrous' substantially iron-freer. asbestos. The catalystis'preferably prepared in the form of lenticular or lamellarshapes so asto present thegreat est possible effective area of catalyst to'the gasstreamf'without at'the same t'imei'rriposing "an" undue resistance togaseous flow; Preferably the 'ratio'of the alkaline earth metalsaltftoithe asbestos is of the order of 2:1 by weight. I a u Thiscatalyst is particularly effective for the refri'o'val' of carbondioxideand oxygen contained in"theindustrialgases referred to and thefollowin'gtabl illustrates the analysis ofan' average: town's gas beforeand after passage. over' they catalyst claimed that application, thefigures quotedbeing -stated as percentages by volume:

Gas analysis" Gas 00, 0, ennui o0 on. H, (bagl'me) Untreated. 3.3 0.62.5 16. 7' '23.8 43.6 4.5 Treated... 0.0 0.0 0.6 21.0 23.8 #15 5.1

I Percent Carbon dioxide 2 5 Oxygen 0.5 1

Unsaturated hydrocarbons 1.5- 3.5

Carbon"monoxide 14 -20 Methane 15- -30 Hydrogen i 45 --55 The balancebeing nitroge V In use the catalyst charged into a. catalyst chamber andthe gases'passed over the catalyst} preferably by' passing themthrough]. a catalyst bed in the chamber; whilst maintaining the catalystat a temperature of about 900,C. The catalyst has a very'satisfactorylife and is readily regenerated by passing air over the exhaustedcatalyst.

In use; the catalyst inthe" container is placed in a furnace and heatedtoa temperature of the order of 900 C. whereafter townsgasis led throughthe catalyst container. The useful life of thecatalyst betweenregenerations for the treatmentof town's gas'of theanalysisquoted in thetable given above is 120. hours for a "gas flovi of '50cubic feet perhour., Under the con ditions .ispecified itwillfbe appreciated thatafter this'tiliie the catalyst is .still capable of re: moving ,most ofthe'carbo'n dioxideand oxygen butnotto'completion'. Underjf 'practicalconditions of working, the temperature of the treatment 'does not varygreatly from 900 C.:' thequantity' of catalyst and the temperature; usedfor a given gas lflow are such, as,'subject to a required useful "lifebefore regeneration, will remove theCOz and O2 effectively without?destroying" considerable amounts of methane. Practical examplesv .willserve to indicate the permissible temperature variation. Using soine 4-5lbs. of the catalyst claimed in our application No. 613,572 in acontainfer'of a volume of from 1 to it at 900C. destruction of methaneis negligible with, agas fiow as low as 10 ft. /hr. If lower gas ratesused then the temperature' should be reduced,- say to 850-'-875 C.Carbon dioxide and oxygen are still removed but the met'hane will crackif the tem peratu're is not reducd, e. g. at 5 ftJ/hr... 2% ofCH4"de'stroyed at "900 0., no CH4 cracking at 850.

, Onthe other hand if thegasfiow i's 50 ftB/hn,

then "at 900 0. the C02 "an'd'bz are completely removed, without CH4cracking, but at 850 C. the residual CO2 will be of the order of 0.5 to0.6%.

The upper limit of the temperature is again dictated by the gas flowused, c. g. at 950 C.

A possible explanation of the catalytic reactions between unsaturatedhydrocarbons, CO2 and 02 results in the elimination of all CO2 and 02with definite decrease in the percentage of unsaturated hydrocarbonsmaking possible an increase in H2 content. The nitrogen figure in thetable is not an estimated figure but constitutes the balance of the gasto a total of 100% and it would be very surprising if these figuresagreed over such a long period. It is believed that they are well withinthe limits of experimental determination. Unless barium carbonate ispresent in the catalyst the CO2 and 02 of the 2 town's gas passesforward. It is probable that the barium carbonate catalyses theformation of CO from C02, 0, and 02. I Y

The regeneration of the catalyst is readily effected by leaving thefurnace heating conditions unaltered, or substantially unaltered, andpassing a stream of air over the catalyst preferably through thecatalyst bed at such a-rate of flow that the catalyst at the inlet end,i. e. that end which the incoming air first meets, does not rise above1100 C. The rise in temperature is due'to exothermic reactions takingplace during the regeneration of the catalyst.

The time of regeneration is of the order of 3 to 4 hours and willnaturally depend upon the 3 degree of fouling or exhaustion of thecatalyst.

After regeneration and when raw towns gas is the gas undergoingtreatment, there is a time lag usually of about 1 hour before theefiluent gas from a catalyst container can be used with safety for gascarburising.

It is important that all metal parts with which the gases come intocontact, such as the inlet and outlet pipes, the grids, supports;thermocouple sheath tubes, battles and other parts of A the catalystcontainer should be constructed of difficultly carburisableheat-resistant materials. The reason for this is that traces of ironlead to a diminution in the methane and carbon monooxide content of thegases and it is this effect which has presented difiiculties in priorprocesses for the removal of carbon dioxide and oxygen from this classof industrial gas.

The accompanying diagrammatic drawing illustrates the following briefdescription of a a justed to give a temperature of the order of 900 C.The outlet 5 from the catalyst container is taken via a cooler 6 to adrying tower in this case packed with silica gel, there being two dryingtowers 1 arranged in parallel with appropriate valves 8 so that thedriers may be used alternately,

one being in use whilst the other is being regenerated. From the dryingtowers the gas is passed through an integrating meter 9 by pipe ID tothe gas carburising furnace" or the like, where it is to be used lnorder to permit of regeneration of the catalyst, valves ll, I2 areinserted respectively in the gas inlet to the compressor and in the gasoutlet from the catalyst chamber so as to isolate those elements of theapparatus from the rest of the plant and a valve 13 in a second inletpipe 14 to the compressor is operated so that the compressor canaspirate air and pass it intothe catalyst container. An outlet pipe l5from the catalyst container (for convenience of definition referred tohereinafter as an air outlet) is opened by operating valve I6 to allowthe gases from the regeneration treatment to escape.

Whilst the foregoing description has been primarily directed to thetreatment/of towns 0 gas it will be understood that it can besuccessfully operated to treat gases used in industry for thepreparation of carburising atmospheres.

We claim:

1. A process of removing carbon dioxide and oxygen from industrial gasescomprising passing the gas over a catalyst consisting of bariumcarbonate extended with substantially iron-free asbestos at a suitabletemperature in the'r'egion of900C.

2. A process of removing carbon dioxide and oxygen from industrial gasescontaining hydrocarbons comprising passing the gas over a catalystconsisting of barium carbonate extended with substantially iron-freefibrous asbestos at a suit- 5 able temperature in the region of 900 C.

3. A process as in claim 2 including periodical regeneration of thecatalyst by passing a stream of air over the catalyst under heatingconditions and at rate of flow such thatthe tempera: ture at the inletend is above 900 C. and does not rise substantially above 1100 C.

4. A process as in claim 2 including periodical regeneration of thecatalyst by passing a stream of air over the catalyst undersubstantially un-' 15 altered heating conditions and at such rate of 0dioxide and oxygen therefrom comprising the steps of compressing thesaid gas, passing" it through a heated catalyst chamber containingbarium carbonate extended on fibrous asbestos, cooling the said gas anddrying the said gas.

6. A process for the treatment of industrial gases as in claim 5 inwhich the catalyst is periodically regenerated by passing a stream ofair over the catalyst under substantially unaltered'heating conditionsand at such a rate of flow that o the temperature at the inlet to'thesaid catalyst chamber does not rise substantially above 1100 C.

FREDERICK WARDLE HAYWOOD. DOUGLAS STUART LAIDLER.

REFERENCES CITED UNITED STATES PATENTS Number Name Date Gutherie et a1Sept. 17. 1940

1. A PROCESS OF REMOVING CARBON DIOXIDE AND OXYGEN FROM INDUSTRIAL GASESCOMPRISING PASSING THE GAS OVER A CATALYST CONSISTING OF BARIUMCARBONATE EXTENDED WITH SUBSTANTIALLY IRON-FREE ABESTOS AT A SUITABLETEMPERATURE IN THE REGION OF 900* C.